This grant proposal is in response to RFA DK 02014 entitled: "Comprehensive Programs in Beta Cell Biology." My laboratory studies mechanisms of transcriptional regulation by nuclear hormone receptors and has recently become interested in the specific role of co-activators in the beta cell based on the study of nuclear targets for insulin signaling. This proposal is responsive to the RFA in several ways: 1) I am a new investigator to the diabetes field interested in transcriptional regulation of the beta-cell by insulin; 2) transgenic and knockout (KO) animal models are proposed to study beta-cell proteins in their physiological context; 3) a study of the role of two co-activators in then-cell, CBP and p300, are proposed; and 4) the role of a beta-cell-specific protein, PDX-1, in insulin-stimulated gene expression and R-cell proliferation will be explored. Regulation of insulin gene transcription in the pancreas involves specific positive and negative cis-acting elements. located in the 5' flanking region. One major regulator of insulin gene expression is the homeobox protein, PDX-1 (also referred to as IPF-1, STF-1, and IDX-1). This protein, first expressed at e8.5 in the mouse, has a major role in pancreatic development and (beta-cell function as demonstrated in both generalized and conditional PDX-1 KO mice; respectively. A second major regulator of both insulin transcription and (beta-cell development is the basic helix-loop-helix (bHLH) protein, NeuroDI43-2, which forms a DNA-binding complex with the ubiquitously expressed E2A proteins. Both PDX-1 and NeuroDI/(3-2 have been shown to interact with the highly related CBP and p300 co-activator proteins. These co-activators have proven to be critical in many aspects of mammalian development, including their function on mitogen-responsive genes; they have also been proposed to be essential for insulin gene transcription based on in vitro studies. It is unclear, however, what role they play in (beta-cell growth and function, and whether their function is constitutive or regulated in the (beta cell. Three Aims are proposed: 1) To-define the role of insulin signaling via the AP-1 complex in proliferative responses of the pancreatic (beta cell; 2) To define constitutive and hormonal regulated interaction domains in CBP and p300 important in the pancreatic (beta cell; and 3) To define the role of CBP and p300 in the adult (beta-cell in mice harboring a cell-specific knock out of either CBP or p300. The overall goal of this proposal will be to determine the mechanism of CBP and p300 action in regulating pancreatic beta-cell growth and function